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Beating Heart Pendant 


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Beating Heart Pendant 

Written By: Quinn Dunki 


Dremel tool (1) 
Hobby knifed) 
Needlenose pliers (1) 
Soldering iron (1) 
Wire strippers (1) 


Resistor (1) 

Resistor (3) 

Resistor (1) 

Capacitor (1) 

Capacitor (1) 

Transistor (1) 

Programmable Unijunction Transistor 

Jewelry bails (3) 

Battery (3) 

Jewelry clasp (1) 

LED (2) 

Solder (1) 

Black felt (1) 

Superglue (1) 

Jewelry chain (2") 



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Page 1 of 7 

Beating Heart Pendant 

While reading through Charles Piatt's excellent book Make: Electronics, I came across this 
nice little circuit for making a gentle pulsing LED. I was struck by the "humanness" of the 
pulse, but couldn't figure out what to do with it. Later I found a heart-shaped tag on some 
pants I had bought, and well, this is the result. I opted to use mainly scrap parts salvaged 
from old computers. I liked the hacky, recycled feel that gave it. 

I took Charles' circuit, and added a second LED for some symmetry. A bob under the 
pendant provides the power. The pendant's chain is part of the circuit, so the clasp becomes 
the on-off switch. 

Step 1 — Beating Heart Pendant 

• Here's the final pendant. Read on for all the gory details! 

• For more details, better pictures, and video of the pendant in action, visit: .. 

© Make Projects 

Page 2 of 7 

Beating Heart Pendant 

Step 2 

• Here's the schematic for the 
Beating Heart. This is taken 
straight from Charles Piatt, with the 
addition of a second LED in 
parallel. The second LED raises 
the average draw of the circuit to 
about 4.5mA. 

Step 3 

• Once the circuit was built and 
tested, I used the aforementioned 
tag from my pants to trace the 
heart shape on the PCB, then cut it 
out with a Dremel. Where the 
schematic shows "chain w/ clasp", 
I've soldered in these silver bails. 
You can find them in the Jewelry 
Findings section of craft stores. 
They are soldered to the PCB for 
structure, and soldered separately 
in to the circuit. Here I'm 
temporarily supplying power via the 
bails to make sure everything is 

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Page 3 of 7 

Beating Heart Pendant 

Step 4 

• Here's the backside. I edged the 
PCB with some insulation that I 
carefully stripped off 16 gauge 
automotive wire and slit down one 
side. I've superglued the edging to 
the PCB. 

• The power supply is composed of 
another silver bail, shaped to hold 
three CR1220 button cells. The bail 
itself is Vss. The back is insulated 
with a scrap of superglued rubber, 
and a wire is glued to that to 
provide ground. The clip hangs 
under the pendant from a 
decorative copper chain (which 
also provides the positive electrical 
connection to the circuit). 

• Three CR1220s should power the 
pendant for about nine continuous 

© Make Projects 

Page 4 of 7 

Beating Heart Pendant 

Step 5 

• For the pendant's chain, I needed 
something that would conduct. I 
tried several different kinds of 
jewelry chain, but couldn't find any 
that conducted reliably when slack 
or in motion. I ended up making my 
own "chain" from scratch by 
unravelling some 16 gauge wire, 
and braiding together three strands. 
The braid is tight and consistent, 
so it looks pretty, and forms a solid 
connection in all conditions. This 
was just like making a friendship 
bracelet in juniour high school. 
Remember those? 

• The far end (not visible in this 
picture) is anchored to one post of 
my bench supply. That was a 
convenient way to hold it firmly so I 
could pull it tight during the braiding 
process. Copper wire is a lot more 
work to braid than thread, but I 
think the end result was worth it. 

© Make Projects 

Page 5 of 7 

Beating Heart Pendant 

Step 6 

• Here's the final chain, ready to 
have clasps attached and ready to 
be fixed to the side bails. 

Step 7 

• The back of the pendant is finished 
with a scrap of black felt. It looks 
clean, and keeps the prickly bits off 
your skin. 

© Make Projects 

Page 6 of 7 

Beating Heart Pendant 

Step 8 

• There you have it! I hope you'll 
make your own, and have some fun 
with the design. 

• If you like this sort of stuff, visit 
for more! 

This document was last generated on 2012-11-03 02:42:30 AM. 

© Make Projects 

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